Gelled fuel compositions



United States Fatent O 3,343,931 GELLED FUEL COMPOSITIONS Carroll F.Doyle, Ellicott City, Md., assignor to W. R. Grace 8: Co., New York,N.Y., a corporation of Connecticut No Drawing. Filed June 24, 1963, Ser.No. 290,255 11 Claims. (Cl. 44-7) The present invention relates to theformation of gels, and more specifically to a novel means by whichnumerous normally fluid fuel compositions may be readily converted intogel form.

It is known that numerous hydrocarbons such as gasoline, kerosene, fueloil, and lubricating oils may be readily gelled through the addition ofgelling agents such as the alkali or alkaline earth metal soaps of longchain fatty acids. The resultant thickened compositions find use aslubricating greases, napalm bomb ingredients, and more recently asrocket fuels.

While the prior art soap thickening agents generally perform adequatelyfrom the standpoint of gel forming ability, it is found that themetallic soaps upon combustion leave an ash residue. For certain usesthe ash residue is objectionable.

It is therefore an object of the present invention to provide a novelmeans for gelling normally liquid fuel compositions.

It is another object to provide a gelled liquid fuel composition whichupon combustion does not leave an ash residue.

It is a further object to provide a novel fuel gelling agent which iseffective for gelling a wide variety of liquid fuels, both of thehydrocarbon and non-hydrocarbon variety.

These and still further objects of the present invention will becomereadily apparent to one skilled in the art from the following detaileddescription and specific examples.

In general, the present invention contemplates a novel means for gellingnormally liquid fuel compositions which comprises admixing from about 1to about 10% by weight of a finely divided polyoxymethylene polymer witha normally liquid fuel composition. The finely divided polyoxymethylenepolymer comprises finely divided fibers Which possess a maximum majordimension i.e., length of about 50 microns, and a length to diameterratio of at least 10:1.

More specifically, I have found that a wide variety of normally fluidfuel compositions may be readily gelled by the addition of about 1 toabout 10% by weight of the finely divided fibrous polyoxymethylenepolymer, the fibers of which are prepared by grinding a polyoxymethylenepolymer which has been produced by the solid state polymerization oftrioxane. The polyoxymethylene polymer which is prepared by the solidstate polymerization and trioxane possesses a highly fibrous structure,and is characterized by possessing a 14 A. identity distance as measuredalong the fiber axis using standard X-ray crystallographic techniques.This polymer may be readily ground using conventional means to formindividual fibers having a thickness (width) of below microns andfrequently below 1 micron. The length of the fibers are preferably below50 microns and frequently fall in the 1 to 5 micron range. This fibrousmaterial possesses a surprising capability of being able to form stablegels when added to numerous fuel compositions. Since the polymer iscomposed of repeating CH O- groups and is 100% combustionable, thegelled fuel composition leaves no ash residue upon burning. Furthermore,the polymer itself possesses considerable fuel value when burned andtherefore contributes for the energy content of the gelled composition.

Liquid fuels which may be treated in accordance with the teachings ofthe present invention are both hydroice carbon and non-hydrocarbon fuelswhich possess melting points below normal ambient temperatures, that isbelow about 0 to 25 C. Typical hydrocarbon fuels which may be gelled arethose hydrocarbons of either an aliphatic or cyclic nature which possessfrom about 6 up to about 18 carbon atoms. Typical examples arecommercially available gasoline, kerosene, fuel oils, and lubricatingoil fractions. Furthermore, hydrocarbons such as benzene, toluene, andn-hexane may be treated. Non-hydrocarbon fuels such as hydrazine andsubstituted hydrazines including symmetrical and nonsymmetrical dimethylhydrazine may also be effectively gelled using the novel gelling agentsset forth herein.

As stated previously from about 1% to about 10% by weight based on thefuel being treated of polyoxymethylene fibers are added. It is foundthat this amount of fibrous polyoxymethylene will produce stable anduseful gels. The precise amount of the present polyoxymethylene fiberswhich are added, depends somewhat on the fuel being treated and theultimate degree of fineness of the polyoxymethylene fibers. It isgenerally found that the more viscous fuels such as heavy residual fueloil or lubricating oil fractions require less polyoxymethylene fiber toprovide a gel of equivalent rigidity. Furthermore, it is found that ifthe polyoxymethylene fibers used have been ground to a very fine degree,that is the polyoxymethylene fibers possess fiber thicknesses in thesub-micron range and maximum lengths of 1 micron or less, lesspolyoxymethylene fibers will produce a desired degree of thickening. Inother Words, it is found the gelling capability of the presentpolyoxymethylene fibers is generally proportional to the fiber fineness.

The present polyoxymethylene gelling agent is added to the fuelcomposition by conventional mixing means. That is, conventionalmechanical mixers including high speed rotary blending devices and sonicgenerator devices may be effectively used. In general, the presentpolyoxymethylene fibers blend quickly and easily with the fuels beingtreated and no special or prolonged mixing procedure is required.

As mentioned above the polyoxymethylene used in the present invention isthat obtained by the solid state polymerization of trioxane. It is foundthe polyoxymethylene produced by this means possesses a unique fibrousstructure which is totally different than that obtained by non-solidstate polymerization of formaldehyde, paraformaldehyde, or trioxane. Thepolyoxymethylene used in the present invention is produced mostconveniently by the polymerization of a solid trioxane which has beeninitiated for polymerization by irradiation with high energy ionizingirradiation. A preferred mode for preparing the presently usedpolyoxymethylene involved (1) irradiating solid trioxaue at atemperature below its melting point with high energy ionizingirradiation; (2) holding the irradiated trioxane at a temperature belowits melting point preferably between 55 and about 61 C. to achievepolymerization; and (3) removing non-polymerized trioxane from thepolymerization mass.

The irradiation step requires from about 0.001 to about 10 megarads ofhigh energy ionizing irradiation to produce the required activatedpolymerization sites. The high energy ionizing irradiation may becomprised of high energy electrons, neutrons, deutrons, alpha particles,

p X-rays and gamma rays. The irradiation may be conducted either in aninert medium or in the atmosphere. However, since trioxane possesses ameasurable vapor pressure at normal ambient temperatures, it isgenerally preferred to contain the trioxane in a closed container duringthe processing procedure.

The polymerization step may be conducted at any temperature in excess of30 C. but below the melting point of the trioxane. Polymerization rateis generally dependcut on the temperature, therefore, a preferredtemperature range for conducting the polymerization is from about 55 to62 C. which is just below the melting point of trioxane. Thepolymerization step is preferably conducted in a closed container toprevent excessive loss of trioxane due to vaporization. Sufficientpolymerization takes place in about 0.5 to about hours, during whichtime a 50% conversion to polyoxymethylene may be readily obtained.

Subsequent to polymerization non-reacted trioxane, which generallycomprises about 50% by weight of the polymerization mass, may beconveniently removed by evaporation or extraction with a solventtherefore, such as water, acetone, or methanol. The extractednon-reacted trioxane may be recycled back intothe polymerization processafter removal of solvents if used.

The polyoxymethylene polymer obtained by this method possesses a uniquecrystalline structure as determined by standard X-ray techniques. It isfound the present polyoxymethylene possesses a 14 A. identity periodalong the fiber axis as compared with the 17 A. identity period foundfor polyoxymethylene prepared by non-solid state prior art methods. Thepresent polymers possess a reduced specific viscosity of from about 0.3to about 3.0 as determined by using 0.1 gram of polymer in 100milliliters of gamma butyrolactone at 135 C. The melting point of thepolymers ranges from about 185 C. to 200 C.

To obtain the finely divided fibrous material which is required for thepractice of the invention, the polymers obtained from the polymerizationprocess subsequent to purification are subjected to a grinding procedurewherein the fibrous material which is formed in cohesive bundles duringthe polymerization is separated and broken to the desired length. Thegrinding may be eifected in conventional grinding or milling apparatuswhich include high speed rotary shearing devices, wet grinding machines,and fluid energy mills. It is generally preferred, however, to use thelatter mentioned fluid energy mill to achieve the degree of grinding andsize reduction required to obtain the desired fibrous gelling material.

It is found the fluid energy mill provides the grinding and millingconditions required to segregate the fibers from the bundles formedduring irradiation and subsequently break them to the desired length.The fibers ob tained possess a thickness or diameter of under 5 micronsand preferably below 1 micron depending on the degree of fibersegregation achieved during milling. The fibers are broken to lengths ofunder 50 microns preferably under 5 microns during the millingoperation. As mentioned previously, the gelling efficiency of thepresent fibrous polyoxymethylene is dependent upon the fineness of thefibrous material. The fineness of the material in turn is largelydependent on the degree of milling which is carried out. In actualpractice, it is found that the highest possible degree of fibersegregation and size reduction is not carried out for economicalreasons. It is frequently found that larger amounts of less finelyground material may be used more cheaply than a smaller amount offibrous material which has been reduced to a near ultimate degree offineness.

The gelled fuel compositions which result from the practice of thepresent invention find numerous uses as propellants for rockets,constituents of napalm bombs and so forth. In general, the presentlygelled fuel compositions may be used for the same purposes prior artgelled fuels are used. The gelled compositions may contain otheringredients such as antioxidants, filling agents, or other additivesnormally found in gelled fuel compositions.

Having described the basic aspects of the present invention thefollowing detailed examples are given to illustrate embodiments thereof.

EXAMPLE I Commercial trioxane crystals were spread out in thin layers ontrays and subjected to 0.5 megarad of 2 mev. electrons. A total of 20kilograms of the irradiated crystals were placed in 16 oz. glass jars.The jars were sealed and submerged in a water bath heated to 55 C. Theheating was continued for 5 hours. At the end of this period, thecontents of the jars were extracted with water to remove the non-reactedtrioxane. The dried polymer remaining after extraction with water wassubsequently dried at room temperature for 24 hours. The dried productweighed 5000 grams and represented a 25% conversion. The RSV of theproduct was determined to be 0.9 as measured in gamma butyrolactone at135 C. using of the gram of the polymer in milliliters of the solvent.

The dried polymer was then milled in a fluid energy mill usingcompressed air as the grinding medium. Milling the product at a rate offrom 20 to 40 grams per minute using an injection pressure of 200p.s.i.g. and a grinding pressure of 250 p.s.i.g. yielded a particulatefibrous product which fell within the desired particle size range.

EXAMPLE II The fibrous polyoxymethylene obtained in Example I wasadmixed with JP-4 jet fuel, RP-l fuel oil, hydrazine and unsymmetricaldimethyl hydrazine by combining the ingredients and manually stirringthe mixture. In all cases it was found that 4% by weight of the finesize polyoxymethylene was sufiicient to combine all the liquid into astable gel. These mixtures remained in the form of a stable gel for aperiod of several weeks at room temperature.

EXAMPLE III To illustrate the ease with which the presentpolyoxymethylene gelling agent may be incorporated in a liquid fuel,three different mixing procedures were used, each of which produced adifferent degree of agitation. (1) Fuel and the fine-sizepolyoxymethylene were combined and manually stirred for approximately 2minutes. (2) Fuel and fine-size polyoxymethylene fibers were mixedtogether in a high speed rotating blade mixing device for 2 minutes. (3)Fuel and fibrous polyoxymethylene were mixed in sonic generatoragitating device which comprised a ring-shaped transducer having aresonant frequency of 6 k.c.p.s. The results are tabulated below.

Fuel POM Mixing Observation (percent) technique 2 1, 2and Stable gel. 41, 2 and Do. 10 1, 2 and Do. 2 1, 2 and D0. 5 1, 2 and Do. 9 1, 2 andD0. 6 1, 2 and Do. 1,2 dimethyl hydrazine 5 1, 2 and D0.

Microscopic examination of all of the gelled products obtained aboveindicated that each of the 3 mixing procedures produce substantially thesame gel formation. Therefore, it is seen that any conventional mixingprocedure may be effectively used.

The above specific examples clearly indicate that stable gel fuelcompositions may be obtained using the fine size fibrouspolyoxymethylene polymers disclosed herein. The use of the presentfibrous polyoxymethylene does not require special mixing procedures, andthe compositions which are formed are totally combustionable.

I claim:

1. A method for gelling liquid fuels which comprises admixing from about1% to about 10% by weight of a finely divided fibrous polyoxymethylenepolymer with a normally liquid fuel selected from the group consistingof hydrocarbons, substituted hydrocarbons, hydrazine, and substitutedhydrazine, said finely divided polyoxymethylene polymer being derivedfrom the solid state polymerization of trioxane and comprising fibershaving a length of less than about 50 microns and the length to diameterratio of at least 10: 1.

2. The method of claim 1 wherein said fuel is a hydrocarbon.

3. The method of claim 1 wherein the fuel is a substituted hydrocarbon.

4. The method of claim 1 wherein the fuel is hydrazine. V a

5. The method of claim 1 wherein the fuel is a substituted hydrazine.

6. A gelled fuel composition comprising a normally liquid fuel selectedfrom the group consisting of hydrocarbons, substituted hydrocarbons,hydrazine, and substituted hydrazine, and from about 1% to 10% by weightof a finely divided fiberous polyoxymethylene polymer derived from thesolid state polymerization of trioxane, the fibers of said finelydivided polymer possessing a major dimension of less than 50 microns anda length to diameter ratio of at least 10: 1.

7. The composition of claim 6 wherein the fuel is a hydrocarbon.

8. The composition of claim 6 wherein the fuel is a substitutedhydrocarbon.

9. The composition of claim 6 wherein the fuel is hydrazine.

10. The composition of claim 6 wherein the fuel is a substitutedhydrazine.

11. The composition of claim 6 wherein said polyoxymethylene polymer isfurther characterized by possessing an identity period of 14 A. asmeasured along the fiber axis.

References Cited UNITED STATES PATENTS 3/1960 Greblick 149-7 X 2/1963Rice.

6. A GELLED FUEL COMPOSITION COMPRISING A NORMALLY LIQUID FUEL SELECTEDFROM THE GROUP CONSISTING OF HYDROCARBONS, SUBSTITUED HYDROCARBONS,HYDRAZINE, AND SUBSTITUTED HYDRAZINE, AND FROM ABOUT 1% TO 10% BY WEIGHTOF A FINELY DIVIDED FIBEROUS POLYOXYMETHYLENE POLYMER LERIVED FROM THESOLID STATE POLYMERIZATION OF TRIOXANE, THE FIBERS OF SAID FINELYDIVIDED POLYMER POSSESING A MAJOR DIMENSION OF LESS THAN 50 MICRONS ANDA LENGTH TO DIAMETER RATION OF AT LEAST 10:1.